Update ProcessKDP and ProcessMachCore to use ConstString plugin
names when specifying the DynamicLoaderDarwinKernel.

ProcessGDBRemote wasn't setting the dyld string any more; remove
the remaining code tracking the dyld plugin name altogether from
that process plugin.


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@181658 91177308-0d34-0410-b5e6-96231b3b80d8